1. Field of the Invention
The present invention generally relates to a CIS (Contact Image Sensor) holder for providing a balanced elastic force to ensure CIS being adjacent to a scanning plate and maintaining a fixed depth of scanning field.
2. Background Description
Scanning devices have been broadly employed to input images. Especially when the personal computer is popular, the scanning device is able to scan a document and thus transform to a digitalized image format. Users can therefore edit, make copies and/or store in a storage device.
Prior known scanning device 1 is shown in FIG. 1. The scanning device 1 includes a body 12, a cover 14, a scanning module 10, a driving rod 18 and a document plate 16. The scanning module 10 is positioned below the document plate 16 and coupled with the driving rod 18. The scanning module 10 is able to move along the driving rod 18. According to the operation of the prior known scanning device, firstly, a document (not shown in the Figures) is placed on the document plate 16. When the cover is closed, the scanning module 10 is driven along the driving rod 18 to the arrow direction. The scanning module 10 is therefore capturing the image of the document and generating digitalized signals.
However, the prior known scanning device is not suitable to the present marketing needs. Users hopes the functions can be enhanced and the size of a scanning device can be minimized dramatically. Thus, a portable scanning device with no functions loss is needed. A minimized portable scanning device can work with a portable notebook to scan documents anywhere and everywhere. In this regard, designers would prefer employing small size Contact Image Sensor (CIS) instead of large size Charged Couple Device (CCD). By employing CIS as a major element, the size of scanning device is able to reduced to acceptable standard. However, since the depth of scanning field of CIS is far short than the depth of scanning field of CCD. If the CIS is unable to closely adjacent to the document plate, the quality of captured images by CIS is not accepted. Therefore, it is very important and causing a big problem to make sure CIS closely adjacent the document plate and moving smoothly.
Regarding the above mentioned problem, there is a known solution. Please see FIG. 2. FIG. 2 shows a cross section of a CIS holding device. The CIS holding device 20 includes a holder 201 and springs 202. The holder 201 contains an opening for receiving CIS 21. The springs 202 are positioned between the CIS 21 and the holder 201 for proving elastic forces to the bottom of CIS 21. By the forces, CIS 21 is able to closely contact upwardly the document plate 16. For an alternative design, there is able to set sliding assistants 210 for reducing friction between the CIS 21 and document plate 16. In this case, the CIS is able to move smoothly when driven by a driving module.
Nevertheless, in the above known solution, since springs are set between the document plate and CIS, it would cause CIS getting jammed if the springs provide unequal forces to CIS. Such situation occurs when the opening of the holder is not projected (produced) balanced that the springs are not compressed equally. In this case, the CIS 21 would get stuck with the document plate, due to elastic forces are not balanced to pus the CIS 21.
It is therefore an object of the present invention to provide an apparatus for holding a CIS closely adjacent to the bottom of a document plate. Thus during scanning processes, the CIS is able to maintain a fixed depth of scanning field.
It is therefore another object of the present invention to provide an apparatus for holding a CIS smoothly movable along the document plate, and avoiding the CIS jammed due to manufacturing differences of CIS holders.